1. Field of the Invention
This invention relates generally to a coalescing assembly for use in a separator and more particularly, but not by way of limitation, to a parallel plate coalescing unit for use in an internally baffled, horizontal-flow oil skimmer.
2. Description of the Prior Art
During the operation of an oil well a mixture of water contaminated with oil and particulate solids is often recovered. For environmental and conservational purposes it is desirable to separate the contaminants from the water prior to discharging the water into the environment.
To remove the oil and particulate solids from the water, separator apparatus known as skimmers or settling tanks have been developed. These separators are often placed upstream of a water polishing apparatus which further cleanses the water. The separators include such types as horizontal vessels having the mixture flow horizontally therethrough, vertical vessels having vertical flow therethrough and vertical vessels having horizontal flow therethrough. Separation of the oil and particulate solids from the water in these types of devices occurs because of the tendencies of the oil to rise and the solids to drop in the water as the mixture flows through the particular separator vessel.
To improve the separation or skimming of the contaminants from the mixture, coalescing means can be placed in the vessels. The coalescing means causes particles of oil to cohere so that larger droplets of oil having faster rise velocities are formed to insure that the oil will rise to the top of the water for being skimmed therefrom within the time it takes the water to flow through and exit the separator vessel.
A coalescing means is disclosed in U.S. Pat. No. 3,957,656 in the name of Castelli. This patent discloses a plate separator comprising horizontally oriented plates being positioned parallel to each other and having corrugations which extend normal to the flow path through the separator vessel. The corrugations on each plate are shaped and positioned relative to those on adjacent plates to provide alternately constricting and expanding fluid passages so that accelerations and decelerations are imparted to the mixture flowing along the plates. Prior to passing through the plate separator, the mixture passes through a flow equalizing baffle including a number of parallel, vertical spaced slats. The Castelli separator apparatus can also include an additional section of separator plates which are separated from the first section of separator plates by coalescing filters. The Castelli patent further discloses that the plates might be made of polypropylene.
The use of a single coalescing means is also disclosed in U.S. patent application Ser. No. 117,680 entitled INTERNALLY BAFFLED, HORIZONTAL FLOW, VERTICAL OIL SKIMMER and filed Feb. 1, 1980 in the name of Warne, Jr. This application discloses a vertical separator vessel in which a fluid mixture is caused to flow along a sinuous horizontal path, and this application mentions that a single coalescing medium can be disposed along the path for coalescing the oil in the mixture.
It has been observed that in a vessel of the type disclosed in the aforementioned Warne, Jr. application, the separation efficiency of the vessel decreases as the flow rate of the mixture through the vessel decreases. An analysis of residence time distribution curves derived from performance data gathered during the testing of an apparatus of the type disclosed in the Warne, Jr. application suggests that short-circuiting may be occurring at the lower flow rates. Short-circuiting is a channeling effect wherein positive flow occurs through only a portion of the cross-section of the total possible flow path.
Therefore, there is the need for an apparatus which can coalesce substances from a mixture and which can overcome the channeling effect detected to exist at relatively low flow rates in at least some types of separator vessels. There is also the need for such an apparatus to aid in the removal of solids from the mixture so that coalescing is not impeded and so that the mixture can be more fully cleansed. Additionally, it is desirable for such an apparatus to more fully remove the desired substances from the mixture so that further polishing of the primary fluid (e.g., water) is unnecessary or is at least aided by the operation of the apparatus. It is also desirable for such an apparatus to be constructed so that it can be located along a single segment of a sinuous flow path of a separator vessel.